GLP-1 peptides explained — semaglutide, tirzepatide, retatrutide, and what researchers are studying

GLP-1 peptides are the most-discussed class on the platform right now, and with good reason — the published research has expanded dramatically over the last three years. This is a beginner-oriented overview of what compounds are in the GLP-1 family, what makes them different from each other, and what researchers in this space are actually studying.

What are GLP-1 receptor agonists?
GLP-1 (glucagon-like peptide-1) is an incretin hormone naturally released by the gut after meals. Native GLP-1 has a half-life of roughly 1-2 minutes, which is far too short for therapeutic use. The class of compounds called GLP-1 receptor agonists are synthetic analogs engineered to mimic native GLP-1 while resisting the enzymatic degradation that breaks down the natural hormone. The result is compounds with half-lives measured in days rather than minutes.

The major compounds researchers are studying.

Semaglutide. The most studied compound in the class. Originally approved as a diabetes therapy under brand names including Ozempic, semaglutide later received approval for weight management at higher doses (Wegovy). The pivotal STEP trials documented sustained weight loss over 68 weeks with substantial cardiometabolic benefits. Half-life is approximately 7 days, supporting once-weekly research dosing protocols.

Tirzepatide. A dual GIP/GLP-1 receptor agonist — meaning it activates both the GLP-1 and the GIP (glucose-dependent insulinotropic polypeptide) receptors. The SURMOUNT trials demonstrated weight loss outcomes that exceeded what semaglutide produced in head-to-head research. The dual-agonist mechanism is currently a subject of active investigation, with the GIP component thought to contribute to nutrient partitioning effects beyond what GLP-1 alone produces.

Retatrutide. A triple agonist (GLP-1, GIP, and glucagon receptor). Earlier-stage research compared to semaglutide and tirzepatide, but published Phase 2 data has shown weight loss outcomes that exceed both. The glucagon-receptor component is hypothesized to contribute additional energy expenditure, but the long-term safety profile is still being characterized. Dosing protocols in published research vary substantially and the consensus is still forming.

Cagrilintide. An amylin analog rather than a GLP-1 agonist, but frequently studied in combination with semaglutide (the combination is sometimes called CagriSema). The combination is being investigated for additive weight loss effects through a different mechanism — amylin slows gastric emptying and modulates satiety signaling separately from GLP-1.

What is being researched.
Beyond the headline weight-management research, current published studies are exploring GLP-1 effects on cardiovascular outcomes (the SELECT trial documented MACE reduction with semaglutide), kidney function (the FLOW trial), addictive behaviors including alcohol and nicotine, inflammation, and a long list of secondary endpoints. The breadth of research is one reason this category dominates the peptide conversation.

What the VialTalk research community tends to focus on.
Comparative outcomes between semaglutide, tirzepatide, and increasingly retatrutide. Dose titration protocols that minimize gastrointestinal side effects. Lean-mass preservation strategies during caloric restriction. The cagrilintide combination question. Vendor quality — counterfeit semaglutide is a real problem in the research-grade supply chain and the Red Flags thread in this category covers the specific patterns to watch for.

Where to go next.
The deeper threads in this category cover specific topics. The semaglutide-vs-tirzepatide thread compares head-to-head research outcomes. The muscle preservation thread covers lean mass strategies. The dose titration thread covers escalation protocols. The Mechanism + Half-Life thread covers the pharmacology in detail. The Quality + COA thread covers what to demand from vendors. The Red Flags thread covers the counterfeit problem specifically.

If you're new to this category, the highest-yield order is the comparison threads on the specific compounds you're interested in, then the dose titration thread, then the quality and red flags threads before evaluating any vendor.